1. Field of the Invention
The invention concerns the manufacture of coil springs, in particular compression coil springs.
2. Description of the Related Art
As is known in the art, coil springs are generally manufactured from a substantially straight wire traveling along a linear path (in practice between drive rollers) to bending fingers that impose on it a curvature corresponding to the diameter of the spring to be produced. Turns are formed in this way that are contiguous unless a beveled tool is inserted to bring about a separation between the turns being formed (when such a tool defines the pitch of the spring, it is sometimes called a “pitch tool”). After the spring formed in this way has reached the required length, the wire is cut; the spring formed in this way is recovered and a new manufacturing cycle is started.
It should be pointed out that, in the conventional way, the insertion of a beveled tool to bring about a non-zero spacing between the adjacent turns is effected in accordance with an alternating to-and-fro movement transversely to the path of the wire. Such an alternating movement is in particular the result of the fact that, in practice, springs with non-contiguous turns, especially compression springs, nevertheless have near their ends end turns that are contiguous to provide a substantially transverse bearing area; thus during the manufacture of such a spring there are times at which the pitch tool must be between the turns and times at which it must be retracted.
As for cutting the wire at the end of the formation of each spring, it is generally brought about by a cutting tool driven with an alternating to-and-fro movement; there has also been proposed a movement of the cutting tool comprising a movement transverse to the wire and a movement tangential thereto, so that the tool moves in a closed loop, substantially retaining a given orientation.
Thus existing machines use both circular movements and translation (linear) movements, and the cycle of forming a spring in practice imposes stopping or at least considerably slowing the wire feed speed at the moment of cutting.
Where linear movements are concerned, these are circular movements converted into linear movements by a complex system of cams, links or direction-changers, to ensure coordinated movements of the pitch and cutting tools, which leads to wear and vibration.
Such vibration and systematically stopping at the time of cutting operations limit considerably the speed of the machine, reduce production quality and lead to high maintenance costs with long down times, whence low productivity.